Dimensions in feet

Dimensions in meters

A = (230/F)*0.305 (meters)

B = A * Vf

C = (A - B)

S = +/- 10cm

R = A * 1.05

The angle of the radials will be idealy between 35° and 45°

Vf (velocoty factor of used coax) depends of the type of cable. Don't trust to much the clasic 0.66 value : the best is to mesure the Vf with a antenna analyser, results are some surprising (espacialy when you use old coax cables).

Applied as there are, those formulas gived me results close to what theoreticaly expected.